Source : Webster's Revised Unabridged Dictionary (1913)

Macrocephalous \Mac`ro*ceph"a*lous\, a. [Macro + Gr. kefalh` the
   head.]
   1. Having a large head.

   2. (Bot.) Having the cotyledons of a dicotyledonous embryo
      confluent, and forming a large mass compared with the rest
      of the body. --Henslow.

Source : WordNet®

macrocephalous
     adj : having an exceptionally large head and brain [syn: {macrocephalic}]